(1) Field of the Invention
The invention relates to a planetary gear for variable transmission towards a tail rotor of a helicopter.
Main and tail rotors of helicopters are coupled to a transmission with a fixed ratio of speeds for said main and tail rotors. Such a fixed ratio of speeds for said main and tail rotors does not correspond to the needs for different flight situations, as for example during level flight almost no thrust is needed from the tail rotor. The operational height of the helicopter is as well limited due to said fixed ratio of speeds for said main and tail rotors, as during hovering in high altitude the rotational speed of the engine(s) of the helicopter has to be increased to speed up the tail rotor with the consequence of increased speed at the main rotor too, such increased speed at the main rotor not being needed.
(2) Description of Related Art
The document EP1 258 658 A2 discloses a transmission apparatus including at least an auxiliary transmission for supplementing a main transmission. The auxiliary transmission includes a damper which has a damper characteristic adapted to a low speed select state of the auxiliary transmission, and which is disposed in a low speed transmission path used for transmission of torque in the low speed select state of the auxiliary transmission. The auxiliary transmission further comprises a bypass member defining a bypass transmission path bypassing the low speed damper. The bypass transmission path is a torque path used for transmission of torque in a high speed select state of the auxiliary transmission.
The document JP 60 107 662 U discloses a transmission.
The document U.S. Pat. No. 5,030,187 A discloses an automatic transmission having a gear train comprising first, second and third single-pinion planetary gear sets. The ring gear (1R) of the first single-pinion planetary gear set is connected integrally or selectively to the carrier (2C) of the second single-pinion planetary gear set, the carrier (1C) of the first single-pinion planetary gear set is connected integrally or selectively to the ring gear (3R) of the third single-pinion planetary gear set, and the sun gear (2S) of the second single-pinion planetary gear set is connected integrally or selectively to the sun gear (3S) of the third single-pinion planetary gear set. The automatic transmission is capable of being placed in any one of at least five forward gears and one reverse gear.
The document EP 0 102 136 A1 discloses an epicyclic change-speed transmission which can include a sequence of either biratio stages, of quadriratio stages, or a combination of both. Each biratio stage has one binary selectable means, one reactive, one input, and one output component Each quadriratio stage has two binary selectable means, two reactive, one input, and one output component. The maximum ratio of the transmission results when the reactive components of the stages are grounded to the casing. When the reactive components of the plurality of stages are coupled to their input and output components in binary logic sequence, and incrementally decreasing variable speed ratio of the input/output members of the transmission will result, that far exceeds the number of stages. The basic stage ratio is defined by the maximum ratio of, and the number of biratio stages in the particularly defined transmission sequence, with the state ratios of the stages being of a particularly defined order. The total number of incremental changes in the ratio of the transmission is also particularly defined.
The document U.S. Pat. No. 3,209,618 A discloses a planetary gear for variable transmission, comprising a first gear set of a first sun gear, a ring gear, first planetary wheels and of a first planet carrier, a plurality of clutches and freewheels for adjustable speeds of the first planet carrier as output and further comprising a second gear set of a second sun gear, a ring gear, second planetary wheels and a second planet carrier.
The document U.S. Pat. No. 5,951,434 A discloses a transmission used as part of a drive unit to transmit power, coupled to a V6 engine drive shaft by a torque converter and includes an axially extending ring gear assembly, a sun gear positioned coaxially within part of the ring gear assembly and two planetary gear assemblies each spaced axially from the other and meshing with the sun gear and the ring gear assembly. The ring gear assembly is driven in rotation about its axis and an output drive shaft by the rotational forces of the motor output shaft and includes two different diameter annular ring gears which are each centered on and extend radially about the transmission axis.
The annular ring gears have different diameters and radially inwardly extending teeth. The sun gear includes a portion axially aligned within each of the two ring gears. A clutch plate or pack, gearing or other band or pressure brake is provided to selectively permit or prevent the rotation of the sun gear about the transmission axis and relative to the output drive shaft. A first planetary gear assembly includes one or more planetary gear pinions meshing with the teeth of the smaller diameter ring gear and its axially aligned portion of the sun gear. The planetary gear pinions are each rotatably mounted to a first planetary carriage which in turn is coupled to the output drive shaft. The second other planetary gear assembly includes at least one second planetary gear pinion meshing with the teeth of the larger diameter ring gear and the portion of the sun gear aligned therein. The second planetary gear pinions are rotatably mounted to pivots coupled to a second gear carriage which in turn is selectively rotatable about the axis. A brake is provided operable to permit or prevent the rotation of one or both of the first planetary gear carriage or the second planetary gear carriage relative to their respective pivots. A second brake provided to selectively lock or unlock the sun gear so as to permit or prevent its rotation relative to the transmission axis.